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Ashley Margret Rasys, Katie Irwin, Sherry Luo, Douglas B Menke, James D Lauderdale; Anolis sagrei lizard—a novel model system for studying fovea development. Invest. Ophthalmol. Vis. Sci. 2018;59(9):589. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The fovea—a pit-like depression in the retina with a high photoreceptor cell density, is specialized area that is important to the vision of primates and many non-mammalian amniotes. However, very little is known concerning the genes and developmental mechanisms that contribute to the formation of the fovea as the eyes of commonly used model systems—like the mouse, chick, frog, and zebrafish lack a fovea. Therefore, we introduce the bifoveated lizard, Anolis sagrei, as a novel model organism for eye-related research. We report here a morphological and histological analysis of foveae development in the lizard as well as highlight functional approaches for gene manipulation in the developing lizard embryo eye.
A. sagrei lizard eggs were collected from our breeding colony and incubated at 27.8°C and 70% humidity. At incrementing time points, embryos were removed from their shells and staged by criteria described by Sanger et al., 2008. Following euthanasia, eyes were removed, processed in Bouin’s fixative, paraffin sectioned, and stained with Hematoxylin and Eosin.
The anole retina exhibits a typical vertebrate architecture consisting of the ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), and retinal pigment epithelium (RPE). In the adult, the center fovea has a substantially larger diameter than that of the temporal fovea, accompanied with higher density of photoreceptor cells (8-10 cells deep in the parafoveal region), and at its core a well-developed pit devoid of retinal cell layers--GCL, INL, and ONL. In contrast, the temporal fovea is approximately half the size of the center fovea, with fewer number of photoreceptor cells (4-5 cells deep at its center), and a much shallower pit that retains all these retinal cell layers. Similar to primates, in lizards the foveae form late in development, occurring during embryonic stages 16-18. At this time, photoreceptor cell packing is underway and by stage 18, the foveae have all of the essential characteristics present in the adult.
This work represents an important step in developing a much needed foveated model organism for eye-related research that is directed towards understanding developmental mechanisms that contribute to fovea formation in vertebrates.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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